[CI] Force php -l failure (#2363)

* [CI] Force php -l failure

By redirecting stderr to a file and checking if the filesize is greater than 0 bytes, we can also force failure for warnings.

See discussion in <https://github.com/FreshRSS/FreshRSS/pull/2362#issuecomment-480623161>.

* exclude JSON lib
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f